Identification of a novel, tissue-specific calpain htra-3; a human homologue of the Caenorhabditis elegans sex determination gene.

We cloned a novel human gene encoding a tissue-specific calpain, termed htra-3, which is highly homologous to the tra-3 sex determination gene of Caenorhabditis elegans. The predicted htra-3 polypeptide had similarity to the calpain large subunits in domain organization throughout domains I to III, but the sequences of domain IV lacked calcium-binding motifs. Northern blot analysis revealed high expression in the colon, small intestine and testis. Radiation hybrid mapping localized the htra-3 gene to chromosome 11q14 (2.53cR apart from WI-3895). Western blot analysis demonstrated that the approximately 73-kDa htra-3 protein was transiently expressed in COS-7 cells. These observations, together with the genetic information in C.elegans, suggest a unique function for htra-3 protein.